2.0) PHASE DIAGRAM • LECTURE OUTLINE: - Define phase diagram, cooling curve, liquidity and solidification. - Connection between cooling curve and phase diagram. - Dissolvable alloy system. - Pure metals,Gibb’s order, lever order ,dual system and eutectic point.
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and solidification.- Connection between cooling curve and phase
diagram.- Dissolvable alloy system.- Pure metals,Gibb’s order, lever order ,dual
system and eutectic point.
Introduction
• Many of the engineering materials possess mixtures of phases, e.g. steel, paints, and composites.
• The mixture of two or more phases may permit interaction between different phases, and results in properties usually are different from the properties of individual phases.
Define Phase Diagram
An equilibrium state of solid system can be reflected in terms of characteristics of the microstructure, phases present and their compositions, relative phase amounts and their spatial arrangement or distribution.
PHASE DIAGRAMS
THEORY AND APPLICATIONS
Some basic concepts
• Phase– A homogeneous region with distinct structure
and physical properties– In principle, can be isolated– Can be solid, liquid or gas
• Phase Diagram– Representation of phases present under a set
of conditions (P, T, Composition etc.)
Concepts…...
• Phase transformation– Change from one phase to another– E.g. L S, S S etc.– Occurs because energy change is negative/goes
from high to low energy state
• Phase boundary– Boundary between phases in a phase diagram
A simple phase diagram
Triple point(Invariant point)
Solid
Liquid
Vapor
Pressure
Temperature
Phase boundary
System: H2O
Gibb’s Phase Rule
P + F = C + 2 P=number of phasesC=number of componentsF=number of degrees of freedom (number of independent variables)